The present invention relates to dichroic dyestuffs for guest-host type liquid crystals and to liquid crystal compositions containing these dyestuffs.
In a guest-host type color display using liquid crystals, a dichroic dyestuff is an essential and indispensable material and the quality of this kind of color display element completely depends upon the characteristics of the dyestuff used.
Under such circumstances, extensive research and development have been made on dichroic dyestuffs; as a result, dyestuffs which seem to be commerically acceptable have been proposed or developed. Typical examples of such dyestuffs include azo dyestuffs as disclosed in Japanese Patent Laid-Open Appln. Nos. 57850/1981, 104984/1981, 2885/1977, etc.
Investigations and developments have been extensively made on elements for guest-host type color displays from a variety of viewpoints, attempting to put these dyestuffs into practical use. Accordingly, it is highly expected that key importance will be attached to such elements in future color displays in terms of both the functionality and fashionability thereof. When compared to conventional color display techniques and peripheral techniques similar thereto which have already been put into practical use, however, such elements are not always better than conventional elements and require further improvements particularly in display characteristics.
Further, in display elements of this type, various modes are known. Among these are, for example, a mode in which one or two polarizing plates are employed and a mode of the so-called White-Taylor type in which no polarizing plate is employed. When the samd dyestuff is employed, the mode in which no polarizing plate is employed is inferior to the mode using a polarizing plate(s), particularly in contrast and appearance. Thus, further improvements in display characteristics are required also in this type.